Time Flies

TIME FLIES AS WE GROW OLDER we’ve probably heard that proclamation uttered many times, whether as a cautionary warning to seize the day or as a weary sigh from our elders. As William James laments on growing old: “the days and the weeks smooth themselves out in recollection to contentless units, and the years grow hollow and collapse”. But why do we perceive time moving faster, and is such a phenomenon a necessity of aging? 

First, what do we mean when we talk about “perceiving time”? Psychologist and neuroscientist Dr. Ernst Poppel breaks down this concept into ‘elementary time experiences’, which include the experience of (1) duration, (2) non-simultaneity, (3) sequence of events, (4) past vs. present, and (5) change. For example, we can identify the sequential order in which an event, for example: ‘water boiling’, takes place (cold water warms up, then simmers, then boils) and the approximate duration of it. Of course, these temporal experiences are by nature highly subjective and variable. Experiencing ‘water boiling’ early in the morning as you’re impatiently waiting to make coffee feels much longer in duration than experiencing the same event while you’re simultaneously running an experiment. When we speak of time perception with regards to aging, we often refer to our experiences of duration and of past and present, both of which are intricately linked and rely heavily on memory and attention.

Memory is a key concept in several philosophical and psychological theories regarding aging’s effect on temporal experience. According to Paul Janet, we perceive duration as a ratio of our lifespan. For example, when you were five years old, one year is 20% of your life; when you’re 76, a year is only 1.32% of your life. This means waiting 24 days for Christmas at age 5 (i.e. 24 days is 1.32% of your life) feels like waiting a whole year at age 76. This mathematical approach complements James’ theory that perceived duration is determined by how memorable life events are. As we grow older, we have fewer new experiences, and familiar events become menial routines that pass by in the blink of an eye. Similarly, Ornstein’s psychological experiments suggest that temporal experience is shaped by the amount of sensory information processed during an event. Thus, children experience time moving more slowly both because their phenomenal world is saturated with new sights and sounds and because their senses are heightened and their faculties attentive. As we grow older, our world becomes familiar, we pay less attention to our environment, and our senses become dull, both biologically and psychologically speaking.

Although perception of time is highly subjective, neurological studies have suggested a biological basis (or at least a biological manifestation) of this phenomenon. Functional magnetic resonance imaging (fMRI) studies point to a dynamic network of cortical-subcortical activation involving several parts of the brain, including that responsible for the circadian rhythm. The neurotransmitters dopamine and norepinephrine also play an integral role: for example, dopaminergic antagonists and agonists slow down and speed up one’s internal clock, respectively. In line with this, studies have shown that aging brains tend to have decreased dopaminergic neurotransmission, suggesting a potential biological explanation for why we perceive time passing faster as we grow older.

Given the role of neurotransmitters in temporal experience, it is not surprising then that time perception is also intricately tied with our emotional states. For example, fear makes us feel time passing more slowly, while excitement speeds up our perception of time. Indeed, anecdotally speaking, we’ve probably experienced time flying when we’re having fun and time crawling when we’re bored. Not only does this suggest that age is not necessarily the main factor in shaping our perception of time, it also implies that it may deserve less recognition than we currently give it.

Although these neurological studies point to a biological component of our subjective temporal experience, it is premature to assert that our perception of time – and particularly how it changes as we age – is biologically deterministic. Firstly, it is important to keep in mind the limitations of such studies: for example, how do we consolidate the firing of neurons with the linguistic content of a subjective experience, and do these studies define “time perception” consistently? Such musings are unfortunately beyond the scope of this article. Secondly, as hinted upon, the tendency to feel “time fly” as we grow old can be influenced by multiple factors, including our emotional and physical health states. Thus, the age-old adage that time flies as we grow old is an oversimplification of a much more complex phenomenon than we realize.

References: 

1. Le Poidevin, R. The Experience and Perception of Time. The Stanford Encyclopedia of Philosophy. Zalta E. N. (ed.) (2015). 
2. Swanson, A. Why half of the life you experience is over by age 7. The Washington Post (2015).
3. Lewis, JG. Why Does Time Fly as We Get Older? Scientific American (2013).
4. Taylor, S. Why Does Time Seem to Pass at Different Speeds? Psychology Today (2011).
5. Rao, SM., et al. The evolution of brain activation during temporal processing. Nature Neuroscience. 4:317-323 (2001).
6. Meck, WH. Affinity for the dopamine D2 receptor predicts neuroleptic potency in decreasing the speed of an internal clock. Pharmacology Biochemistry and Behavior. 25(6):1185-1189 (1986).
7. Backman, L., et al. The correlative triad among aging, dopamine, and cognition: Current status and future prospects. Neuroscience & Biobehavioral Reviews. 30(6):791-807 (2006).
8. Gozlan, M. A stopwatch on the brain’s perception of time. The Guardian (2013). 

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Pailin Chiaranunt

Pailin is a PhD student in the Department of Immunology at the University of Toronto. She works in Dr. Arthur Mortha's laboratory on creating a high-dimensional map of host-microbiome interactions in the intestine. In her spare time, Pailin enjoys traveling, reading philosophy, and dabbling in martial arts and languages.

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